The former Republican congressman and three-time presidential candidate Ron Paul has launched a scathing attack on what he calls a US-backed coup in Ukraine, insisting the Crimean people have the right to align their territory with Moscow and characterising sanctions against Russia as “an act of war”.

He also said providing economic aid to Ukraine was comparable to giving support to rebels in Syria knowing it would end up in the hands of al-Qaida.

The libertarian guru’s remarks in an interview with the Guardian are almost diametrically opposed to those of his son, the Republican presidential hopeful Rand Paul, who has called for stiff penalties against Russia and declared: “If I were president, I wouldn’t let [Russian president] Vladimir Putin get away with it.”

Ron Paul, who retired from his Texas congressional seat in 2012, has always adopted a sceptical view of US foreign interventions. He said that although the US had not been involved in any military overthrow of the government in Kiev, it had facilitated a coup in the sense of “agitating” elements who wanted to usurp Ukraine’s former president, Victor Yanukovych.

“The evidence is pretty clear that the NGOs [non-governmental organisations] financed by our government have been agitating with billions of dollars, trying to get that government changed,” he said. “Our hands are not clean.”

There is broad bipartisan support on Capitol Hill for the movement that brought about the departure of Yanukovych, as well as criticism of Putin for Russia’s military intervention in Crimea, which many view as a prelude to annexing the territory.

A Russian-backed referendum, in which Crimeans will be asked if they want to align their government with Moscow, will take place on Sunday, although western leaders argue the poll has no legitimacy or legal basis.

Paul said Crimeans should be allowed to break away from Kiev.

“I think everyone should have right to express themselves,” he said. “It is messy, that is for sure, because two big governments are very much involved in trying to tell the Ukranians what to do.”

However he said Russia had a more justifiable basis for being involved in Crimea than the US, and no government should prevent locals on the peninsula from determining their future.

“That is our how our country was started,” he said. “It was the right of self-determination, and voting, and asking and even fighting for it, and seceding. Of course libertarians were delighted with the secession of the various countries and units of government away from the Soviet Union, so yes, we want the people to make the decisions.”

He added: “The people of Ukraine would probably have a loose-knit association, with a rather independent east and west, and an independent Crimea. It would work quite well.”

“Now we’re getting involved with the Europeans in trying to change the government of Ukraine,” he said. “Now they want our money. It is just like when we when we go out and try and throw out [Syrian president Bashar al-] Assad, we end up working with al-Qaida. Now we’re likely to give money to Ukraine so they can pay their bills to Russia. That is the insanity of it all.”

His son, an increasingly strong contender for the Republican presidential nomination, made a similar point in the Senate on Thursday, when he voted against a bill providing aid to Ukraine.

The Kentucky senator is far more pragmatic than his father, however, and is on a mission to recast his reputation as a mainstream potential commander-in-chief. This week, he used an op-ed piece in Time magazine to exhibit his foreign policy credentials, adopting a tough stance against Moscow.

“Vladimir Putin’s invasion of Ukraine is a gross violation of that nation’s sovereignty and an affront to the international community,” he wrote. “His continuing occupation of Ukraine is completely unacceptable, and Russia’s president should be isolated for his actions.”

He added: “Economic sanctions and visa bans should be imposed and enforced without delay.”

Ron Paul with his son Rand, at a 2011 presidential campaign event. Photograph: Charles Dharapak/AP

His father took the opposite view. “I think sanctions are horrible. They’re acts of war,” he told the Guardian.

“It is based on a moral principle of theft. They want to target sanctions against 20 or 30 bad Russians who they claim have committed a crime against humanity, and therefore we’re going to freeze their assets and steal them from them.”

When it was suggested his position was opposite to that of his son, Paul replied: “Neither he nor I have ever pretended our views are identical. He still has the most libertarian views in the Senate.”